1. Field of the Invention
The present invention relates generally to medical devices and methods. More particularly, the present invention relates to improved systems and methods for removing or draining cerebral spinal fluid (CSF) from a subarachnoid or CSF space of a patient to control intracranial pressure (ICP) and/or modulate CSF hydrodynamics to treat hydrocephalous and other diseases.
Hydrocephalus is a condition characterized by an elevated ICP resulting from excessive production or retention of CSF in the patient's CSF space (as defined hereinafter). Hydrocephalus is commonly treated by implanting a shunt to provide controlled drainage of the CSF from the CSF space. In particular, the shunt comprises a tube having one end implanted in the patient's cerebral ventricles and another end implanted in a location outside of the CSF space to which the CSF can be drained, such as the peritoneum. The shunt typically comprises a control valve positioned along its length to control flow based on the differential pressure between the ventricles and the peritoneum. As excess CSF accumulates in the CSF space, the pressure in the ventricles and elsewhere increases. The control valve of the shunt is typically arranged to open when the differential pressure exceeds some threshold value. Thus, the shunt acts as a pressure relief system for the CSF space including the subarachnoid spacing (as defined hereinbelow).
Although quite successful for treating hydrocephalus, such shunts can have problems under certain circumstances. In particular, because the amount of CSF drained from the ventricles depends on the differential pressure across the control valve, patient position can have a significant effect on the amount of fluid being drained. In some instances, too much CSF can be drained causing the patient's ICP to fall below desirable levels. The problem arises because conventional hydrocephalus shunts have valves which control the differential pressure across the valve. While excessive production or inadequate drainage of CSF is one cause of the pressure building up in the ventricles, changes in patient position will also affect the differential pressure. The control valve has no way of distinguishing between these two sources of pressure variation, so the valves must be set to operate at a control pressure point which is a comprise between maintaining a target pressure in the ventricles and providing a margin of safety so that the valve will not drain excess CSF in response to patient movement. Moreover, other safety devices often must be added to the hydrocephalus shunts to further protect the patients, such as anti-gravity devices, and the like. With all these precautions, it is very difficult to maintain the target pressure in the ventricles and over drainage and under drainage of the CSF frequently occurs.
For these reasons, it would be desirable to provide improved systems and methods for controlling ICP in order to treat hydrocephalus and other conditions associated with elevated ICP or excessive production of CSF and other conditions associated with compromised CSF drainage and hydrodynamics. In particular, such systems and methods should remove CSF in a manner which is not dependent on patient position or posture and more closely maintain a natural ICP. Such systems and methods would thus provide for maintenance of ICP within more desirable physiologic levels, and should reduce the risk of over and under drainage of CSF and excessive lowering of ICP. Still more desirably, such systems and methods could be implemented in a variety of ways, including mechanically, hydraulically, electronically, and combinations thereof. At least some of these objectives will be met by the inventions described hereinbelow.
2. Description of the Background Art
Conventional devices for draining CSF in response to baseline ICP are described in numerous prior patents, including U.S. Pat. Nos. 3,889,687; 3,985,140; 3,913,587; 4,375,816; 4,377,169; 4,385,636; 4,432,853; 4,532,932; 4,540,400; 4,551,128; 4,557,721; 4,576,035; 4,595,390; 4,598,579; 4,601,721; 4,627,832; 4,631,051; 4,675,003; 4,676,772; 4,681,559; 4,705,499; 4,714,458; 4,714,459; 4,769,002; 4,776,838; 4,781,672; 4,787,886; 4,850,955; 4,861,331; 4,867,740; 4,931,039; 4,950,232; 5,039,511; 5,069,663; 5,336,166; 5,368,556; 5,385,541; 5,387,188; 5,437,627; 5,458,606; PCT Publication WO 96/28200; European Publication 421558; 798011; and 798012; French Publication 2 705 574; Swedish Publication 8801516; and SU 1297870. A comparison of the pressure-flow performance of a number of commercially available hydrocephalus shunt devices is presented in Czosnyka et al. (1998) Neurosurgery 42: 327–334. A shunt valve having a three-stage pressure response profile is sold under the Orbis-Sigma® tradename by Nitinol Medical Technologies, Inc. Boston, Mass. 02210 (formerly by Cordis). U.S. Pat. No. 5,334,315, describes treatment of various body fluids, including cerebrospinal fluids, to remove pathogenic substances therefrom. Articles discussing pressures and other characteristics of CSF in the CSF space include Condon (1986) J. Comput. Assit. Tomogr. 10:784–792; Condon (1987) J. Comput. Assit. Tomogr. 11:203–207; Chapman (1990) Neurosurgery 26:181–189; Magneas (1976) J. Neurosurgery 44:698–705; Langfitt (1975) Neurosurgery 22:302–320.